1. Field of the Invention
The present invention relates to an image forming apparatus, and more particularly to liquid application technology that can be used desirably for depositing a treatment liquid on a recording medium prior to the deposition of an ink by means of an inkjet recording apparatus in order to promote aggregation of a color material of the ink, for example.
2. Description of the Related Art
In order to realize a high quality printing by an inkjet recording apparatus, the technology is known in which a treatment liquid, such as multivalent metal salt solution or acid aqueous solution, is deposited on a recording medium prior to depositing an ink thereon, so that the treatment liquid reacts with the ink on the recording medium so as to prevent the breeding or color mixture of the ink.
Japanese Patent Application Publication No. 2005-225065 discloses a liquid application apparatus comprising a mechanism depositing a treatment liquid on a recording medium. The mechanism includes: an application roller serving as an application member applying the treatment liquid to the recording medium; and a liquid holding member holding the application liquid in a liquid holding space which is formed by causing the liquid holding member to abut against the surface (roller surface) of the application roller. According to this liquid application apparatus, by rotating the application roller, the application liquid held in the liquid holding space is supplied to the surface of the application roller while the application liquid is transferred from the application roller to the recording medium.
In this liquid application apparatus, when it is determined that an application operation is not carried out for some time after the end of the previous application operation, then the application liquid is restored from the liquid holding space so as to prevent the application roller from being immersed in the application liquid for a long time and reduce the deterioration of the application roller caused by the application liquid.
However, according to the liquid application apparatus disclosed in Japanese Patent Application Publication No. 2005-225065, a restore flow channel (second flow channel) for restoring the treatment liquid in the liquid holding space to a storage tank is opened into the treatment liquid layer of the storage tank (i.e. below the liquid surface of the treatment liquid). Therefore, when the treatment liquid restoring operation is carried out for the liquid holding space, the treatment liquid is sent to the treatment liquid layer of the storage tank at the initial phase, and then the air trapped via an air connection port that is connected with a supply flow channel (first flow channel) is sent to the treatment liquid layer of the storage tank together with the treatment liquid from the middle phase to the end phase. In this way, the air is trapped in and mixed with the treatment liquid in the storage tank, thereby oxidizing the treatment liquid in the storage tank. As a result of the oxidation of the treatment liquid, the aggregation of the ink based on the reaction with the treatment liquid becomes insufficient, and it becomes difficult to prevent the breeding or color mixture of the ink sufficiently.
Moreover, similar phenomena can occur during the filling operation of the treatment liquid into the liquid holding space. More specifically, during the filling operation, until the treatment liquid is filled into the liquid holding space and the flow channels, the air existing in parts thereof is sent into the treatment liquid layer of the storage tank. Therefore, as in the case of the filling operation, the air is trapped in and mixed with the treatment liquid in the storage tank, thereby oxidizing the treatment liquid in the storage tank. In particular, the progression of the oxidation of the treatment liquid is more rapid during the filling operation than that during the restoring operation, which can lead to noticeable phenomena.